Object Oriented Programming is at least as much a state of mind as a set of programming language facilities. When I learnt C++ it was a bit difficult to get used to writing object-oriented programs but now that I've been doing it for many years I can't get used to thinking about my programs any other way.
I was writing some PHP code recently and (not knowing about PHP classes) started writing it in a procedural fashion. After a while I noticed that many of the functions I was writing started to fall naturally into classes (with a first parameter that gave the function context). So it was only natural to re-write it in object-oriented style once I figured out how to do so.
In the process of doing so, I found lots of bugs in my original code (which I had thought was rather nifty). Many functions became much simpler. I also found it was much easier to do various optimizations that would have been very difficult to do without classes (such as minimizing the number of database queries). My code file did become somewhat bigger, but I attribute this to the extra indentation most lines have, and the fact that PHP requires you to write "$this->" everywhere.
I also tried writing a C program (from scratch) for the first time in a very long time a while ago. I found myself using an object-oriented style and implementing vtables as structs.